1. Field of the Invention
This invention relates to electronic circuit technology, and more particularly, to a capacitive keyboard device which is designed for integration to an electronic unit, such as mobile phone or calculator, for use as a data input device, and which has a keystroke triggering threshold adaptively adjustable capability that can adaptively adjust the keystroke triggering threshold of the capacitive keyboard device.
2. Description of Related Art
Capacitive keyboards are a type of data input device that operates on a change in capacitance to determine whether a key has been pressed down by the user. This data input function is based on a compressible capacitor structure whose capacitance can be changed to a smaller value when compressed. Therefore, when a key is pressed down by the user, the capacitor will be compressed and thus reduced in capacitance, resulting in a change in the voltage charged on the capacitor, thus triggering the generation of a key strobe signal.
In construction, all the structural and electronic parts of a capacitive keyboard are covered under a thin plastic sheet. This feature allows the capacitive keyboard to be well protected against external contamination and abrasion. Moreover, since the capacitive keyboard has no moving parts as conventional mechanical-type of keyboard, it can be constructed with a smaller size. This feature allows capacitive keyboards to be particularly welcome and widely used on small-size portable devices.
In practical application, however, one drawback to the capacitive keyboard is that its keystroke triggering threshold to the user's key-pressing actions might be unreliable for long period of use, due to the reason that the rated capacitance of the capacitor structure might gradually decay to a smaller value by some internal and external factors, such as long time of use, abrasion, decay of the capacitor structure, temperature and humidity, and noise interferences. Moreover, the keystroke triggering threshold of the capacitive keyboard can also be influenced by various user factors, such as user's finger size, user's habitual key-pressing actions, and water or oil moistened on the user's finger.
All of the above-mentioned factors would affect the keystroke triggering threshold of a capacitive keyboard. There exists therefore a need in the electronic industry for a new technology that can adaptively adjust the keystroke triggering threshold of the capacitive keyboard in despite of the influencing factors mentioned above.